1. Field of the Invention
The present invention is directed to the field of antennas used in wireless communication devices and particularly to adaptive tuning of such antennas.
2. Description of the Prior Art
There has been a proliferation in recent years in the field of wireless telecommunications. Items such as cordless and cellular telephones, pagers, wireless modems, wireless email devices, personal digital assistants (PDAs) with communication functions, and other mobile communication devices are becoming commonplace, particularly among individuals who need to be quickly contacted from remote locations. With such devices, it is very important to maintain a clear, strong signal that preserves the integrity of the transmission.
The antennas used with previous wireless communication devices are prone to many significant problems. Some devices, such as pagers and cellular telephones, are usually worn on the person of the user. However, the human body has certain inherent dielectric properties that create an electromagnetic boundary. The boundary conditions of the body of the user change the surrounding impedance, affecting the antenna current distribution and the signal radiation pattern, thus lowering the gain of the antenna by about 4 dB. In this way, the antenna is xe2x80x9cdetunedxe2x80x9d. Antenna detuning may also be caused by the presence of certain objects such as metallic bodies and also various ground plane conditions. This effect results in a shorter operating radius and poor in-building performance for some wireless communications devices.
Such boundary effects can be particularly pronounced in modern mobile communication device designs, in which embedded antennas are common. A signal transmitted from or received by an antenna which is integrated into a communication device may encounter several boundaries, including for example a printed circuit board, a battery, a display screen, a device housing, a device carrying case and any of a multitude of other elements or components associated with the device, in addition to a user""s body. All such boundaries affect signal propagation and the surrounding impedance seen by the antenna.
Previous devices also suffer from performance problems related to the polarization characteristics of transmission and reception signals. Electromagnetic radiation propagates in any plane and can thus be regarded as having vertical and horizontal polarizations. In order to receive a strong signal, an antenna must be property aligned with the polarization plane of the incoming signal. However, when a mobile device is in operation, it may be turned in all different directions and may not be optimally aligned to receive an incoming signal. In a two-way device, transmissions from the device can be affected by a similar problem. Known device antennas incorporate a loop design, which is nominally effective at implementing the two polarizations but suffers from low gain and low bandwidth. Boundary sources also affect the reception of a polarized signal.
At least a portion of the signal power losses associated with antennas in wireless devices is due to signal reflection. Ideally, all of the signal power of a signal input to an antenna should be converted into an output signal. In reference to FIG. 1, all of the power in a signal generated by a communication unit 12 in a wireless communication device 10 and input to an antenna 16 through a line 14 would ideally be radiated out into the air by antenna 16. A communication signal received over the air by antenna 16 would similarly be converted into a received signal and input to the communication unit 12. However, in reality the characteristic impedance of the communication unit 12 and line 14 interacts with the characteristic impedance of the antenna 16. Unless these impedances are equal, some signal reflection will occur at the interface between line 14 and antenna 16.
One known method of addressing the above-noted problems is to provide an impedance matching circuit between communication circuitry and an antenna, as shown in FIG. 2. Communication device 20 is substantially the same as device 10, but includes impedance matching circuit 24 in line 14. As will be apparent to those skilled in the art to which the invention pertains, impedance matching circuit 24 will normally be an LC circuit with inductance and capacitance elements connected in any one of a number of standard matching circuit topologies. On the communication unit side of line 14, characteristic impedance is relatively easily determined in accordance with known techniques. For example, line 14 may be a coaxial cable having a standard characteristic impedance of 50 xcexa9, in which case the impedance matching circuit 24 would be designed and implemented such that the overall impedance of the matching circuit 24, in conjunction with the characteristic impedance of the antenna 16, is also 50 xcexa9.
A major problem with impedance matching in mobile or other wireless communication systems is that impedance matching circuits are normally calibrated during device manufacture and do not normally provide for adjustments in the field, whereas surrounding impedance affecting antennas is rarely constant. In the example receiver 20, over the air signals transmitted and received by antenna 16 may encounter such dielectric boundaries as the housing of device 20, printed circuit boards on which the communication unit 12 is built, electronic components in the communication unit 12, batteries for powering the device 20, display 18, input device 22 and the body of a device user, all of which will affect the impedance seen by the antenna 16. Such impedances can be estimated, but are dependent upon the orientation of the device with respect to its surroundings. Thus, even the best estimates of impedance matching requirements cannot possibly remain accurate for all device operating conditions.
Another known technique intended to compensate for signal reflection effects is shown in FIG. 3. The device 30 is similar to devices 10 and 20, but includes signal power measurement and amplifier control arrangements in addition to the impedance matching circuit 24. The arrangement shown in FIG. 3 is normally used only in a transmit signal path, as indicated by the illustrated unidirectional connections between components. In FIG. 3, a signal generated in communication unit 12 for transmission from device 30 is amplified by power amplifier 26 and then fed to directional power coupler 28. The transmission signal is split between the impedance matching circuit 24 and a termination 34. A reflected signal induced by the combination of antenna 16 and matching circuit 24 is then fed back to a signal power measurement unit 32, which develops an amplifier control signal. Such conventional arrangements measure only signal magnitude and are not designed or intended to determine signal phase. Since effective antenna and surrounding impedances are dependent upon orientation of the antenna, phase information can be important for accurate impedance matching. Furthermore, instead of correcting the underlying problem causing signal power losses, these conventional systems merely boost signal power so that the signal losses can be tolerated.
Therefore, there remains a need for an improved impedance matching arrangement and technique. According to the invention, surface acoustic wave (SAW) technology is used to determine the magnitude and phase of reflected signals and thereby impedance magnitude and phase in a wireless communication device. The determined magnitude and phase are then used to develop control signals which are advantageously used to adjust components in an impedance matching circuit to thereby provide adaptive tuning in a communication device.
It is an object of the invention to provide an improved impedance matching method and system which provide for an increased operating radius for a wireless communication device.
A related object of the invention is to provide a wireless communication device with improved performance in physically congested operating environments, such as within buildings.
It is a further object of the invention to provide an impedance matching method and system that render a wireless communication device less sensitive to environmental fluctuations.
The inventive method and system also enable a wireless communication device to operate with less sensitivity to directional position.
According to an aspect of the invention, a method for adaptive tuning in a wireless communication device comprises the steps of determining magnitude and phase differences between impedance of a matching circuit and an impedance to be matched and adjusting the impedance of the matching circuit to compensate the differences.
The determining step preferably comprises the steps of providing a first IDT track comprising a first input IDT configured to produce a SAW output when excited by an electrical input signal, a first output IDT configured to produce an electrical output signal when excited by a SAW input, and a first terminated IDT positioned adjacent to the first input IDT and the first output IDT and configured to produce a SAW output when excited by an electrical input signal and an electrical output signal when excited by a SAW input, providing a first termination circuit connected to the first terminated IDT and causing the first terminated IDT to reflect a SAW toward the first output IDT responsive to a SAW produced by the first input IDT, applying an electrical input signal to the first input IDT to produce a first SAW, and receiving a first electrical output signal produced by the first output IDT in response to a first reflected SAW produced by the first terminated IDT responsive to the first SAW. The first electrical output signal may then be processed to determine impedance magnitude and phase of the first termination circuit. When the first termination circuit is the impedance matching circuit, the determining step may further comprise the step of comparing the impedance magnitude and phase of the first termination circuit with a predetermined magnitude and phase of the impedance to be matched to thereby determine the magnitude and phase differences.
In an embodiment of the invention, the determining step further comprises the steps of providing a second IDT track comprising a second input IDT configured to produce a SAW output when excited by an electrical input signal and a second output IDT configured to produce an electrical output signal when excited by a SAW input, and a second terminated IDT positioned adjacent to the second input IDT and the second output IDT and configured to produce a SAW output when excited by an electrical input signal and an electrical output signal when excited by a SAW input, providing a second termination circuit connected to the terminated IDT and causing the second terminated IDT to reflect a SAW toward the second output IDT responsive to a SAW produced by the second input IDT, applying an electrical input signal to the second input IDT to produce a second SAW, and receiving a second electrical output signal produced by the second output IDT in response to a second reflected SAW produced by the second terminated IDT responsive to the second SAW.
In such a multiple IDT track embodiment, the first termination circuit may be the impedance matching circuit, the second termination circuit may be a reference circuit having known impedance, and the determining step may then further comprise the steps of frequency down converting the first electrical signal by mixing the first and second electrical output signals to generate a mixed signal and low pass filtering the mixed signal to generate a filtered signal, and processing the filtered signal to determine impedance magnitude and phase of the first termination circuit. The magnitude and phase differences may be determined by comparing the impedance magnitude and phase of the first termination circuit with a predetermined magnitude and phase of the impedance to be matched.
The first input IDT and the first output IDT may comprise a first input/output IDT having first electrical input/output terminals, such that the step of applying an electrical input signal to the first input IDT comprises the step of applying the electrical input signal to the first electrical input/output terminals and the step of receiving a first electrical output signal comprises the step of receiving the first electrical output signal from the first electrical input/output terminals. The second input IDT and the second output IDT may similarly comprise a second input/output IDT having second electrical input/output terminals, such that the step of applying an electrical input signal to the second input IDT comprises the step of applying the electrical input signal to the second electrical input/output terminals and the step of receiving a second electrical output signal comprises the step of receiving the second electrical output signal from the second electrical input/output terminals.
A method according to the invention may further comprise the steps of providing a third termination circuit and switchably connecting either the first termination circuit or the third termination circuit to the first terminated IDT. The first termination circuit may be the impedance matching circuit, the third termination circuit may be the impedance to be matched, and the determining step may further comprise the steps of connecting the first termination circuit to the first terminated IDT, applying an electrical input signal to the first input IDT to produce the first SAW, receiving the first electrical output signal, connecting the third termination circuit to the first terminated IDT, applying an electrical input signal to the first input IDT to produce a third SAW, and receiving a third electrical output signal produced by the first output IDT in response to a third reflected SAW produced by the first terminated IDT responsive to the third SAW. The first and third electrical output signals may then be processed to determine the magnitude and phase differences. Alternatively, the first termination circuit may be the impedance matching circuit, the second termination circuit may be the impedance to be matched, and the determining step comprises the steps of processing the first electrical output signal to determine impedance magnitude and phase of the first termination circuit, processing the second electrical output signal to determine impedance magnitude and phase of the second termination circuit, and comparing the impedance magnitude and phase of the first termination circuit and the impedance magnitude and phase of the second termination circuit to determine the magnitude and phase differences.
When a third termination circuit is to be used, the determining step may instead comprise the further steps of providing a third IDT track comprising a third input IDT configured to produce a SAW output when excited by an electrical input signal and a third output IDT configured to produce an electrical output signal when excited by a SAW input, and a third terminated IDT positioned adjacent to the third input IDT and the third output IDT and configured to produce a SAW output when excited by an electrical input signal and an electrical output signal when excited by a SAW input, providing a third termination circuit connected to the terminated IDT and causing the third terminated IDT to reflect a SAW toward the third output IDT responsive to a SAW produced by the third input IDT, applying an electrical input signal to the third input IDT to produce a third SAW, and receiving a third electrical output signal produced by the third output IDT in response to a third reflected SAW produced by the third terminated IDT responsive to the third SAW.
In a preferred triple-track embodiment, the first termination circuit is the impedance matching circuit, the second termination circuit is a reference circuit having known impedance, the third termination circuit is the impedance to be matched, and the determining step comprises the steps of frequency down converting the first and third electrical output signals by mixing the first and second electrical output signals to generate a first mixed signal, mixing the second and third electrical output signals to generate a second mixed signal and low pass filtering the first and second mixed signals to respectively generate a first filtered signal and a second filtered signal, and processing the first filtered signal and the second filtered signal to determine the magnitude and phase differences.
An adaptive tuning system according to an aspect of the invention comprises a passive SAW device, means for supplying an electrical input signal to excite the passive SAW device, means for processing electrical output signals produced by the SAW device responsive to the electrical input signals to generate a control signal, and an adjustable impedance matching circuit connected to receive the control signal, the impedance of the impedance matching circuit being dependent upon the control signal.
In one embodiment, the passive SAW device comprises a first IDT track, the first track including a first input IDT configured to produce a SAW output when excited by an electrical input signal, a first output IDT configured to produce an electrical output signal when excited by a SAW input, a first terminated IDT positioned adjacent to the first input IDT and the first output IDT and configured to produce a SAW output when excited by an electrical input signal and to produce an electrical output signal when excited by a SAW input, and a first termination circuit connected to the first terminated IDT and causing the first terminated IDT to reflect a SAW toward the first output IDT responsive to a SAW produced by the first input IDT, the magnitude and phase of the reflected SAW being dependent on the first termination circuit. In this embodiment, the first input IDT produces a first SAW in response to an electrical input signal from the means for supplying and the first output IDT produces a first electrical output signal in response to a first reflected SAW produced by the first terminated IDT responsive to the first SAW.
The adjustable impedance matching circuit may be connected as the first termination circuit, and the means for processing may then generate the control signal based on a comparison between the first electrical output signal and a predetermined signal. The predetermined signal is preferably dependent upon an impedance to be matched by the impedance matching circuit.
The passive SAW device may further comprise a second IDT track, the second track including a second input IDT configured to produce a SAW output when excited by an electrical input signal, a second output IDT configured to produce an electrical output signal when excited by a SAW input, a second terminated IDT positioned adjacent to the second input IDT and the second output IDT and configured to produce a SAW output when excited by an electrical input signal and to produce an electrical output signal when excited by a SAW input, and a second termination circuit connected to the second terminated IDT and causing the second terminated IDT to reflect a SAW toward the second output IDT responsive to a SAW produced by the second input IDT, the magnitude and phase of the reflected SAW being dependent on the second termination circuit. The second termination circuit may be an impedance to be matched by the impedance matching circuit. This impedance to be matched may be known or unknown.
The first input IDT and the first output IDT may comprise a single first input/output IDT and the second input IDT and the second output IDT may similarly comprise a single second input/output IDT.
According to a further embodiment of the invention, the first termination circuit is switchably connected to the first terminated IDT in the first IDT track, such that any one of a plurality of different termination circuits may be switchably connected to the first terminated IDT. The plurality of different termination circuits preferably includes the impedance matching circuit and an impedance to be matched by the impedance matching circuit.
In a still further embodiment, the passive SAW device further comprises a third IDT track, the third track including a third input IDT configured to produce a SAW output when excited by an electrical input signal, a third output IDT configured to produce an electrical output signal when excited by a SAW input, a third terminated IDT positioned adjacent to the third input IDT and the third output IDT and configured to produce a SAW output when excited by an electrical input signal and to produce an electrical output signal when excited by a SAW input, and a third termination circuit connected to the third terminated IDT and causing the third terminated IDT to reflect a SAW toward the third output IDT responsive to a SAW produced by the third input IDT, the magnitude and phase of the reflected SAW being dependent on the third termination circuit. The third input IDT produces a third SAW in response to an electrical input signal from the means for supplying, and the third output IDT produces a third electrical output signal in response to a third reflected SAW produced by the third terminated IDT responsive to the third SAW.
In further preferred embodiments of the invention, the system further comprises a frequency down converter, the converter comprising mixers for mixing the first and second electrical output signals and a reference frequency signal to generate a mixed signals and low pass filters for filtering the mixed signals to generate a down converted signals. In such embodiments, the means for processing generates the control signal based on the down converted signals. The reference frequency signal may be supplied by either an oscillator or, in multiple-track embodiments, by one of the IDT tracks.
According to an aspect of the invention, each IDT is configured to operate at a predetermined frequency equal to a frequency at which a communication device sends or receives communication signals. The impedance matching circuit is preferably connected to an antenna of the device.
Communication devices in which adaptive tuning methods and systems according to the present invention may be implemented include, but are in no way limited to, such devices as cordless telephones, mobile communication devices, cellular telephones, wireless modems, hand-held electronic communication devices, pagers and personal digital assistants (PDAs) enabled for communications.
Further features of the invention will be described or will become apparent in the course of the following detailed description. As will be appreciated, the invention is capable of other and different embodiments, and its several details are capable of modifications in various respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive.